Hypochlorous acid process

ABSTRACT

A process for producing hypochlorous acid by reacting an aqueous solution of an alkali metal hydroxide in droplet form with gaseous chlorine to produce hypochlorous acid vapor and solid alkali metal chloride particles in which the improvement comprises employing molar ratios of gaseous chlorine to the alkali metal hydroxide of at least about 22:1. 
     The process achieves high yields of hypochlorous acid by minimizing side reactions including the formation of chlorate as an impurity in the alkali metal chloride particles produced. 
     The hypochlorous acid solution produced contains from about 35 to about 60 percent by weight of HOCl, a dissolved chlorine concentration of less than about 2 percent by weight, and is substantially free of alkali metal ions and chloride ions.

This application is a continuation-in-part of Ser. No. 07/264,667, filedOct. 31, 1988, now abandoned, and is a continuation-in-part of Ser. No.07/153,303, filed Feb. 8, 1988, now abandoned.

This invention relates to an improved process for producing concentratedhypochlorous acid solutions which are essentially free of ionicimpurities.

Hypochlorous acid has been used in the preparation of available chlorinecompounds such as calcium hypochlorite, chloramines, andchloroisocyanuric acid compounds.

Previous methods of hypochlorous acid preparation have included thosewhich react chlorine gas with water or an aqueous solution of an alkalimetal hydroxide to form dilute aqueous solutions of hypochlorous acid oran alkali metal hypochlorite. These dilute aqueous hypochlorous acidsolutions, which contain chloride ions and may contain alkali metalions, are concentrated by distillation. Processes using this method aredescribed by E. P. McElroy in U.S. Pat. No. 1,510,790, Oct. 7, 1924; inBritish Patent No. 543,944, published Mar. 20, 1942; and by C. C.Crawford et al in U.S. Pat. No. 2,347,151, Apr. 18, 1944.

These references also mention condensing the HOCl distillate to recoverthe hypochlorous acid but provide no details of the condensation.

However, distillation of hypochlorous acid or hypochlorite solutions inthe presence of chloride ions as practiced in the above processesresults in the formation of chlorate ions by decomposition of HOCl and asubstantial reduction in the yield.

U.S. Pat. No. 1,748,897, published by Oppe on Feb. 25, 1930, describes aprocess for preparing a solid mixture of alkali metal hypochlorite andalkali metal chloride by reacting chlorine gas with a spray of alkalimetal hydroxide, while cooling the reactants and product to effectcondensation. The product of this technique is a solid mixture of alkalimetal hypochlorite and alkali metal chloride, which has very limitedutility.

More recently, a process has been described in U S. Pat. No. 4,146,578,issued Mar. 27, 1979 to J. P. Brennan et al in which hypochlorous acidvapor is produced by spraying an aqueous alkali metal hydroxide indroplet form or solid alkali metal hydroxide particles into gaseouschlorine. The process is operated using excess amounts of chlorine toalkali metal hydroxide including those up to about 20 times thestoichiometric amount. The reaction is conducted at temperatures whichvaporize the hypochlorous acid as it forms to separate the hypochlorousacid vapors from the solid alkali metal chloride particles. Thehypochlorous acid vapors are then scrubbed with water to produce ahypochlorous acid solution. The scrubbing is generally carried out attemperatures in the range of 0° to 30° C., however, Brennan et al teachthat at temperatures below about 9.6° C. there is a tendency to formsolid chlorine octahydrate which precipitates in the scrubber.

Moreover, scrubbing the hypochlorous acid vapors in water reduces theconcentration of the hypochlorous acid product.

To achieve high yields of hypochlorous acid in processes which reactchlorine gas with droplets of an alkali metal hydroxide, it is necessaryto minimize side reactions including the formation of chlorate as animpurity in the alkali metal chloride particles produced.

In addition, it is desirable to produce solid alkali metal chlorideparticles which have low moisture concentrations as these particles canbe readily recovered from the reactor and the scaling or caking ofreactor surfaces or components with salt is minimized.

Further, to produce highly concentrated solutions of hypochlorous acidit is necessary to limit the amount of water present in the process.

An object of the present invention is to provide a process for producingincreased yields of hypochlorous acid vapors.

Another object of the present invention is to provide a process forproducing hypochlorous acid vapors and solid alkali metal chlorides inwhich the solid alkali metal chloride particles have low concentrationsof chlorate.

An additional object of the present invention is to provide a processfor producing hypochlorous acid vapors and solid alkali metal chlorideparticles having low concentrations of moisture.

Yet another object of the present invention is to provide a process forproducing highly concentrated aqueous solutions of hypochlorous acidwhich are free of ionic impurities.

These and other advantages are accomplished in a process for producinghypochlorous acid by reacting an aqueous solution of an alkali metalhydroxide in droplet form with gaseous chlorine to produce hypochlorousacid vapors and solid alkali metal chloride particles in which theimprovement comprises employing molar ratios of gaseous chlorine to thealkali metal hydroxide of greater than about 22:1.

More in detail, the process is carried out in a suitable reactor such asone provided with means for spraying discrete droplets of an aqueoussolution of an alkali metal hydroxide into the reactor; means forfeeding gaseous chlorine into the reactor; means for withdrawing solidalkali metal chloride product from the reactor; and means forwithdrawing a gaseous mixture comprised of hypochlorous acid, chlorinemonoxide, unreacted chlorine and water vapor from the reactor.

The reactor and/or reactant feed lines are provided with suitableheating means for maintaining the reaction mixture at a temperaturesufficiently high to vaporize the hypochlorous acid product and waterand to dry the alkali metal chloride particles.

Any alkali metal hydroxide capable of reacting with gaseous chlorine toform hypochlorous acid may be employed as a reactant in the process ofthis invention. Typical examples of suitable alkali metal hydroxidesinclude sodium hydroxide, potassium hydroxide, lithium hydroxide andmixtures thereof. Sodium hydroxide is the preferred reactant since theresulting sodium chloride by-product is more easily disposed of than theother alkali metal chlorides.

As gaseous mixtures having high concentrations of hypochlorous acid andchlorine monoxide are desired, highly concentrated aqueous solutions ofthe alkali metal hydroxide are used. Suitable concentrations includethose in the range of from about 40 to about 80, and preferably fromabout 45 to about 60 percent by weight of alkali metal hydroxide.

The alkali metal hydroxide solution is sprayed from at least oneatomizer preferably positioned at or near the top of the reactor.

The atomizer is preferably positioned along the central axis of acylindrical reactor, to provide minimum contact between the atomizeddroplets and the walls. The atomizer may be directed up, down, sidewaysor any other orientation that meets the above conditions.

Droplet sizes are selected which permit a substantially completereaction of the droplets of alkali metal hydroxide with chlorine, thevaporization of hypochlorous acid and water produced and the productionof substantially dry alkali metal chloride particles having lowconcentrations of chlorate.

The dry alkali metal chloride particles produced, while smaller than theoriginal droplets, are preferably sufficiently large enough to prevent asignificant portion of the particles from being entrained in the gaseousmixture produced.

Typical atomizing techniques of the pneumatic, hydraulic, and spinningdisc type, among others, which are suitable for use in the process ofthis invention, are described in the monograph entitled "Atomization andSpray Graining" by W. R. Marshall, Jr., Chemical Engineering ProgressMonograph Series, No. 2, Volume 50, 1954. A gas, such as chlorine gas,under pressure may be used to atomize droplets of aqueous alkali metalhydroxide by premixing before discharge from the nozzle, or the liquiddroplets and chlorine gas are mixed after discharge from theirrespective nozzles. The chlorine gas which reacts with the alkali metalhydroxide may be fed directly to the reactor/or mixed with an inert gassuch as air or nitrogen before being fed to the reactor.

The process of the present invention is conducted at temperatures whichare sufficiently high to vaporize the hypochlorous acid as it is formed.Vaporization of the hypochlorous acid and water present provideseffective separation from the alkali metal chloride particles produced.The alkali metal particles recovered are substantially dry and have lowconcentrations of chlorate as an impurity. Generally temperatures in therange from about 75° C. to about 150° C., and preferably from about 90°to about 140° C. at atmospheric pressure or less are employed. In apreferred embodiment, the gaseous mixture of chlorine and chlorinemonoxide being recycled to the reactor is heated as this provides bettercontrol of the reaction temperature.

Generally, the pressure in the reactor ranges from about 2 to about 100psia, and preferably from about 10 to about 20 psia. However, higher orlower pressures may be employed if desired.

The reaction time between gaseous chlorine and the droplets of alkalimetal hydroxide to produce hypochlorous acid is virtually instantaneous.

The reactions which take place during operation of the process of theinvention can be illustrated by the following equations:

    Cl.sub.2 +NaOH→HOCl(g)+NaCl(s)                      (1).

    3Cl.sub.2 +6NaOH→Na(ClO.sub.3)+5NaCl+3H.sub.2 O     (2)

To suppress the formation of chlorate as illustrated by equation (2),suitable excess amounts of chlorine gas are employed. These excessamounts include those in which the molar ratio of chlorine to alkalimetal hydroxide is at least about 22:1. For example, excess amounts ofchlorine may include molar ratios from 22:1 to about 200:1, preferablyfrom about 25:1 to about 100:1, and more preferably from about 25:1 toabout 50:1.

The novel process of the invention reacts chlorine gas with droplets ofan alkali metal hydroxide which initially have a high pH. Upon contactwith the chlorine gas the pH at the surface of the droplet is reduced.The use of high molar ratios of chlorine to alkali metal hydroxide isbelieved to result in a reduction of the pH on the surface of thedroplet to a range in which the formation of hypochlorous acid on thesurface of the droplet is promoted. Thus a large excess of chlorine usedpromotes the process of equation (1) above resulting in the formation ofthin films of hypochlorous acid on the droplet surface which readilyevaporate. At lower molar ratios of chlorine to alkali metal chloridethe pH on the surface of the droplet is raised and the formation ofhypochlorite ions which further react to produce chlorate, the reactionof equation (2) is promoted. Excesses of chlorine are employed whichresult in a pH on the surface of the alkali metal hydroxide droplet inthe range of from about 1 to about 5, and preferably from about 2 toabout 4.

These large excesses of chlorine gas thus result in increased yields ofhypochlorous acid as the formation of chlorate is suppressed and itsconcentration in the alkali metal chloride particles reduced to lessthan about 10 percent by weight, and preferably less than about 6percent by weight. In addition, the use of large excesses of chlorinegas provide an improved method of maintaining the reaction temperaturein the reactor for producing the gaseous mixture.

In a continuous process, the gaseous mixture of hypochlorous acid vapor,water vapor, chlorine gas, and chlorine monoxide gas produced in thereactor is removed from the reactor and passed through a solidsseparator to remove any fine particles of alkali metal chloride whichmay be present.

The gaseous mixture comprised of hypochlorous acid vapor, chlorinemonoxide, chlorine, and water vapor used in the process of the presentinvention contains high concentrations of HOCl and Cl₂ O. The chlorinemonoxide is formed by the conversion of HOCl vapors during thevaporization process according to the equation:

    2HOCl←→Cl.sub.2 O+H.sub.2 O                    (3)

To produce highly concentrated hypochlorous acid solutions, theconcentration of water in the gaseous mixture is maintained in the rangeof from about 10 to about 25 mole %, and preferably at from about 13 toabout 20 mole %. In a preferred embodiment substantially all of thewater vapor present in the gaseous mixture removed from the reactor isprovided by the aqueous solution of alkali metal hydroxide employed inthe reaction.

The gaseous mixture may also contain fine particles of the alkali metalchloride which are entrained. Fine particles may be removed by anysuitable separation means, for example, by passing the gaseous mixturethrough a gas filter medium or through a solid separator such as acyclone.

Moist solid particles of alkali metal chloride entrained in the gaseousmixture of hypochlorous acid or present during the concentration ofhypochlorous acid reduce the yield of hypochlorous acid, and ifdissolved in the hypochlorous acid solution product lower the stabilityof the solution.

The solids-free gaseous mixture is fed to a condenser. The condenser isoperated at temperatures which produce concentrated aqueous solutions ofhypochlorous acid without condensing undesirable amounts of chlorine orliquid chlorine monoxide. Surprisingly, it has been found that thegaseous mixture can be condensed at temperatures well below those atwhich solid chlorine hydrates are normally formed without precipitatingthese solid compounds or forming ice crystals in the hypochlorous acidsolution.

Suitable temperatures for operating the condensation process includethose in the range of from about -5° C. to about +20° C., preferably atfrom about -5° C. to about +10° C. and more preferably in the range offrom about 0° to about 5° C. at pressures of about 3 to about 10 torr.The condensation of the gaseous mixture can be operated at higher orlower pressures if desired.

The novel concentrated hypochlorous acid solutions produced are highlypure and have improved stability. The dissolved chlorine concentrationin the hypochlorous acid solution of the present invention is less thanabout 2 percent, and preferably less than about 1 percent by weight. Theconcentrated hypochlorous acid solution is substantially free of ionicimpurities such as alkali metal, chloride, and chlorate ions.Concentrations of the chloride ion are less than about 50 parts permillion; the alkali metal ion concentration is less than about 50 partsper million; and the chlorate ion concentration is no more than about100 parts per million.

The hypochlorous acid solutions recovered from the condenser have aconcentration in the range of from about 35 to about 60, and preferablyfrom about 40 to about 55 percent by weight of HOCl. The highlyconcentrated solutions have densities, for example, in the range of fromabout 1.15 to about 1.26, preferably from about 1.17 to about 1.24, andmore preferably of from 1.19 to about 1.23 grams per milliliter (gm/ml)at a temperature in the range of from 10° to 15° C. The novel solutionsof the present invention have a golden color which deepens as theconcentration of HOCl increases.

The uncondensed gaseous mixture recovered from the condenser issubstantially anhydrous. While the chlorine monoxide concentration issignificantly reduced, the chlorine gas concentration is substantiallythe same as that in the original gaseous mixture fed to the condenser.

As the process of the present invention is preferably operatedcontinuously, the uncondensed gaseous mixture is returned to the reactorwhich generates the HOCl--Cl₂ O gaseous mixture, preferably afterpassing through a heat exchanger to raise the temperature.

Employing large excess amounts of chlorine in the process of theinvention provides the gas mixture for recycle with increased stabilityand safety in operation as it minimizes the chance of an explosion ofgaseous chlorine monoxide which can be initiated by a spark or heat.Thus, it is desirable to maintain chlorine monoxide concentrations ofless than about 40 percent, and preferably less than 30 percent, forexample, from about 5 to about 25 percent by volume in the gaseousmixture of chlorine and chlorine monoxide for recycle. Theseconcentrations are readily achieved by employing molar ratios ofchlorine gas to the alkali metal hydroxide of at least about 22:1.

Employing large excess amounts of chlorine gas produces dry solidparticles of alkali metal chloride having low concentrations of moistureand minimal amounts of chlorate as an impurity. The alkali metalchloride particles can be removed readily from the reactor and resultsin reduced scaling or caking of salt on reactor surfaces or components.

The process of the invention further results in high yields ofhypochlorous acid vapor as only small amounts of the product react toproduce the chlorate impurity.

The concentrated aqueous hypochlorous acid solution produced by thenovel process of the present invention can be used as a bleaching orsanitizing agent. Further, according to the invention, the concentratedhypochlorous acid can be employed in the production of chloroisocyanuricacid compounds such as dichloroisocyanuric acid or trichloroisocyanuricacid by feeding the concentrated HOCl solution to a reactor containingcyanuric acid or an alkali metal cyanurate. For example, the productionof trichloroisocyanuric acid by the reaction of hypochlorous acid withcyanuric acid is represented by the following equation:

    3HOCl+C(O)NH--C(O)--NH--C(O)--NH←→3H.sub.2 O+C(O)--NCl--C(O)--NCl--C(O)--NCl

Likewise, calcium hypochlorite, a commercial sanitizing and disinfectingagent for water bodies such as swimming pools, can be produced inaccordance with the invention by reacting a slurry of lime with theconcentrated hypochlorous acid solution. Similarly the production ofhighly pure alkali metal salts of hypochlorous acid can be produced,including sodium hypochlorite and lithium hypochlorite. In addition, theconcentrated hypochlorous acid solutions can be employed as thehypochlorinating agent in improved processes for the production ofchlorohydrins and other chlorinated organic compounds.

To further illustrate the novel process of the present invention, thefollowing example is presented without the intention of being limitedthereby. In the examples the concentration of hypochlorous acid vaporand chlorine monoxide gas in the gaseous mixture have been combined andreported as chlorine monoxide.

EXAMPLE 1

Sodium hydroxide solution having 50% by weight of NaOH was continuouslyfed to an atomizer located in the upper portion of a cylindricalreactor. The atomizer sprayed droplets of sodium hydroxide solution, thedroplets being smaller than 250 microns in size, into a gaseous mixtureof chlorine maintained at a temperature of 98° C. The molar ratio ofchlorine to sodium hydroxide in the reaction mixture was maintained at30:1 to provide sufficient chlorine to completely react with the sodiumhydroxide to produce hypochlorous acid vapor and dry solid sodiumchloride particles. The larger particles of sodium chloride settled inthe bottom of the reactor. A gaseous mixture having an averageconcentration of 19.2 parts by volume of chlorine monoxide gas(including hypochlorous acid vapor), 65.1 parts by volume of chlorine,15.7 parts by volume (15.7 mole percent) of water vapor, and fineparticles of dry sodium chloride was continuously removed from thereactor and passed through a cyclone. The fine particles of sodiumchloride were recovered in the cyclone and the gaseous mixture fed to avertical shell and tube heat exchanger maintained at a temperature ofabout 0° C. and a pressure of about -28 torr gauge. A portion of thechlorine monoxide gas and substantially all of the water vapor wascondensed to produce an aqueous hypochlorous acid solution. Anuncondensed gas mixture containing an average of 20.7 percent by volumeof chlorine monoxide gas, 78.9 percent by volume of chlorine and, 0.4percent by volume of water vapor was continuously removed from thecondenser. The uncondensed gas mixture was passed through a heatexchanger to raise the temperature to about 140° C. The heated gaseousmixture of Cl₂ O and Cl₂ was fed to the reactor to supply a portion ofthe chlorine gas required as the reactant.

A solution of hypochlorous acid was recovered from the condenser havingan average concentration of 49.7 percent by weight of HOCl. Theconcentrated HOCl solution contained about 0.4 percent by weight ofdissolved chlorine. A yield of 80 percent based on sodium hydroxide wasobtained. Solid salt particles recovered from the reactor had an averageconcentration of 5.9 percent by weight of chlorate and had a moisturecontent of 1 percent by weight.

EXAMPLE 2

A gaseous mixture containing an average concentration of 180.7 parts byweight of chlorine monoxide, 384.5 parts by weight of Cl₂, and 60.3parts by weight of water vapor was continuously passed through a cycloneseparator to remove any entrained solid particles of alkali metalchloride. The solid-free gaseous mixture at a temperature of 85°-90° C.was passed through a vertical shell and tube heat exchanger maintainedat a temperature of about 0° C. and a pressure of about 3-4 torr tocondense a portion of the chlorine monoxide and substantially all of thewater vapor to produce an aqueous hypochlorous acid solution containing45 to 50 percent by weight of HOCl. The hypochlorous acid solution had apH of about 1 and the dissolved chlorine concentration was determined tobe about 1 percent by weight. An uncondensed gas mixture containing anaverage of 141.9 parts by weight of Cl₂ O, 384.1 parts by weight of Cl₂,and 0.5 parts by weight of water was continuously removed from thecondenser. The uncondensed gas mixture was passed through a heatexchanger to raise the temperature to about 100° C. and recycled to agenerator used to produce the gaseous mixture of chlorine monoxide.

EXAMPLE 3

The process of Example 1 was repeated and a hypochlorous acid solutionproduced containing 51.42% by weight of HOCl.

EXAMPLE 4-7

A concentrated hypochlorous acid solution containing 44.91% by weight ofHOCl was produced by the process of Example 1. Aliquots (10 ml) of thissolution were stored in constant temperature baths at 10° C. and 15° C.Hypochlorous acid solutions having concentrations of 39.93% HOCl, 34.96%HOCl, and 33.57% HOCl were also prepared by dilution of the 44.91% HOClsolution with deionized water and aliquots stored in the constanttemperature baths. The density of the concentrated solutions wasdetermined by weighing an aliquot (to 0.0001 g). The results, given inTable I below, are the average of three determinations for eachconcentration.

COMPARATIVE EXAMPLES A,B,C, AND D.

The procedure of Example 3 was repeated using hypochlorous acidsolutions containing 29.48%, 24.2%, 19.65% and 10.5% by weight of HOClprepared by dilution of the 44.91% HOCl solution. The results are givenin Table I below:

                  TABLE I                                                         ______________________________________                                        Density of Hypochlorous Acid Solutions:                                                  HOCl Concn.   g/ml     g/ml                                        Example No.                                                                              (% by weight) at 10° C.                                                                       at 15° C.                            ______________________________________                                        4          44.91         1.192    1.191                                       5          39.93         1.171    1.163                                       6          34.96         1.147    1.14                                        7          33.57         1.144    1.138                                       Compare A  29.48         1.118    1.115                                       Compare B  24.2          1.098    1.095                                       Compare C  19.65         1.079    1.076                                       Compare D  10.5          1.036    1.034                                       ______________________________________                                    

EXAMPLES 8-10

The optical absorbance of a concentrated hypochlorous acid solution(45.0 wt. % HOCl, reddish yellow in color) was determined at a wavelength of 550 nm using a 5 cm. quartz cell at 25° C. on a UV-visiblespectrophotometer (Perkins Elmer, Model 303). The solution was dilutedwith distilled water to obtain concentrations of 40% and 35% by weightof HOCl. The optical absorbance of each of these solutions was similarlydetermined. The solutions took on a more yellowish color as dilutionincreased. The chlorine monoxide content of the HOCl solutions wascalculated using the following formula;

    WT % Cl.sub.2 O=k[WT % HOCl].sup.2 /d.

where K=1.12×10⁻³ and d=density. The value of the factor is based on theknown quantification constant for hydrolysis of Cl₂ O.

The results are given in Table II below:

COMPARATIVE EXAMPLES E AND F

The concentrated hypochlorous acid solution of example 7 was furtherdiluted with distilled water to provide hypochlorous acid solutionshaving 22.5 and 11.25% by weight of HOCl. The procedure of Example 7-9was repeated and the results are given in Table II below:

                  TABLE II                                                        ______________________________________                                               Concentr. Density         Absorbance                                                                            Cl.sub.2 O                           Example                                                                              Wt. %     g./ml     HOCl  @ 550 nm                                                                              Wt. %                                Number HOCl*     (10° C.)                                                                         M/L   (cm)    (0° C.)                       ______________________________________                                         8     45.0      1.19      10.2  0.112   2.4                                   9     40.0      1.17      8.9   0.056   1.9                                  10     35.0      1.15      7.7   0.034   1.4                                  Comp. E                                                                              32.0      1.14      7.0   0.025   1.2                                  Comp. F                                                                              22.5      1.10      4.7   0.09    0.58                                 Comp. G                                                                              11.25     1.05      2.1   0.08    0.14                                 ______________________________________                                         *Total of HOCl and Cl.sub.2 O expressed as HOCl.                         

While the invention has been described above with reference to specificembodiments thereof, it is apparent that many changes, modifications andvariations can be made without departing from the inventive conceptdisclosed herein. Accordingly, it is intended to embrace all suchchanges, modifications and variations that fall within the spirit andbroad scope of the appended claims. All patent applications, patents andother publications cited herein are incorporated by reference in theirentirety.

What is claimed is:
 1. A process for producing hypochlorous acidsolutions which comprises:a) reacting droplets of an aqueous solution ofan alkali metal hydroxide with gaseous chlorine in a reaction mixture inwhich the molar ratio of chlorine to the alkali metal hydroxide is atleast about 22:1, b) vaporizing the reaction mixture to separate agaseous mixture comprised of hypochlorous acid vapor, chlorine monoxidegas, chlorine gas, and water vapor from solid particles of an alkalimetal chloride, c) condensing the gaseous mixture to produce a solutionof hypochlorous acid and an uncondensed gaseous mixture comprisingchlorine and chlorine monoxide, d) separating the uncondensed gaseousmixture from the solution of hypochlorous acid, and, e) feeding theuncondensed gaseous mixture to step a).
 2. The process of claim 1 inwhich the concentration of water vapor in the gaseous mixture comprisedof hypochlorous acid vapor, chlorine monoxide gas, chlorine gas, andwater vapor is from about 10 to about 25 mole percent.
 3. The process ofclaim 2 in which the reaction temperature is maintained in the range offrom about 75° to about 150° C.
 4. The process of claim 3 in which themolar ratio of gaseous chlorine to the alkali metal hydroxide is from25:1 to about 200:1.
 5. The process of claim 1 in which the alkali metalhydroxide is selected from the group consisting of sodium hydroxide,potassium hydroxide, lithium hydroxide, and mixtures thereof.
 6. Theprocess of claim 5 in which the alkali metal hydroxide is sodiumhydroxide.
 7. The process of claim 5 in which the molar ratio ofchlorine gas to alkali metal hydroxide is from about 25:1 to about200:1.
 8. The process of claim 7 in which the reaction temperature ismaintained in the range of from about 90° to about 140° C.
 9. Theprocess of claim 8 in which the molar ratio of chlorine to sodiumhydroxide is from about 30:1 to about 60:1.
 10. The process of claim 4in which the aqueous solution of alkali metal hydroxide hasconcentrations of from about 40 to about 80 percent by weight of alkalimetal hydroxide.
 11. The process of claim 10 in which the hypochlorousacid solution contains from about 35 to about 60 percent by weight ofHOCl.
 12. The process of claim 1 in which the concentration of chlorinemonoxide in the uncondensed gaseous mixture is from about 5 to about 25percent by volume.
 13. The process of claim 12 in which the uncondensedgaseous mixture is heated to a temperature in the range of from about75° to about 150° C.
 14. The process of claim 1 in which the gaseousmixture is condensed at a temperature in the range of from about -5° toabout +10° C.
 15. The process of claim 14 in which the gaseous mixtureis condensed at temperatures in the range of from about -5° to about +5°C.
 16. The process of claim 15 in which in which the water vaporconcentration in the gaseous mixture is from about 13 to about 20 molepercent.
 17. The process of claim 16 in which the hypochlorous acidsolution contains from about 40 to about 55 percent by weight of HOCl.18. The process of claim 1 in which, prior to step c), the gaseousmixture is passed through a separation means.
 19. The process of claim12 in which the solid alkali metal chloride particles have a chlorateconcentration of less than about 10 percent by weight.
 20. The processof claim 19 in which the solid alkali metal chloride particles have amoisture content of less than about 1 percent by weight.
 21. The processof claim 18 in which the separation of the solid particles of alkalimetal chloride employs as a separator means a gas filter medium or acyclone.
 22. The process of claim 21 in which the alkali metal chlorideis sodium chloride.
 23. The process of claim 21 in which the separatormeans is a cyclone.